Patent GB-546591-A (GB)
Title: Improvements in or relating to brakes
IPC: F16D65/22
Filed: 1940-07-10
Abstract: 546,591. Fluid-pressure operated drum brakes. BUDD WHEEL CO. July 10, 1940, Nos. 11518 and 11519. Convention dates, July 19, 1939 and May 25, 1940. [Class 103 (i)] [Also in Group XXVI] In brakes of the kind comprising a pair of brake shoes that are applied by a pair of opposed pistons in a common cylinder, the cylinder is provided with means acting on the pistons for adjusting them and the shoes. There may be a pair of cylinders each with a pair of pistons actuating adjacent ends of the shoes so that both shoes are self-energising irrespective of the direction of rotation of the drum or one cylinder may be provided with a single piston so that only one shoe is self-energising for both directions of drum rotation. The brake shown in Figs. 1, 2 comprises a pair of cylinders 23 each containing a pair of pistons 9 each having a cavity 8 within which is received the ends 7 of the shoes 6. The inner ends of the piston are reduced as shown to provide annular spaces between the pistons and the cylinder into which enter passages 23 which as regards the upper cylinder are connected to the pressure fluid supply pipe 25 and in the case of the lower cylinder provides bleed passages normally closed by a plug 45. The two cylinders are connected by passages 26 and pipe 28. The inner faces of the pistons are shaped to engage an adjusting conical wedge 34 provided with a stem screwing into the cylinder and a squared end 37 whereby the wedge may be moved axially. The wedge is guided by a projection 41 on a plug 42 secured into the cylinders instead of the cavity 8, the piston may be provided with a vertical slot curved in side view to receive the correspondingly shaped shoe end. The shoes are guided by resilient members 15 secured to the back plate and bearing against the shoe webs. Mechanical means for applying the shoes comprises a lever 47 pivoted at 49 on one shoe and connected by a pin-and-slot 50 to a link 52 which is pivoted at 54 to the other shoe. The lever 47 is operated by a cable 56. The link is channelled at 55 to clear the release spring. In another construction, Figs. 7, 8 each cylinder is formed with shoulders at 124 for engagement with the outer enlarged ends of the pistons and which limit the inward movement of the pistons. The inner ends of the pistons are provided with sealing rings 130 and each inner face is formed with an annular recess which when the faces are initially in contact form together an annular channel 131 the cross-section of which is substantially that of the passage 132 through which the pressure liquid is supplied whereby trapping of air during the filling or bleeding operation is prevented. The cylinders are connected by the pipe 135 and bleeding is effected through the passage 136 normally closed by the plug 137. The lower cylinder is provided with an adjusting device comprising a pair of obliquely disposed slidable rods 139 adapted to engage the piston ends and operated by a coned plug 142 screwed into the cylinder casting and having a series of facets upon which the ends of the rods bear thus holding the cone against undesired rotation. The shoe ends are free to slide radially on the piston ends. In operation, with the drum rotating in the direction indicated, the lower end of the left-hand shoe and the upper end of the righthand shoe anchor through the respective pistons and the shoulders 124 or the rods 139, while with the opposite direction of drum rotation the diametrically opposite ends of the shoes anchor. Both shoes are thus self energising irrespective of the direction of drum-rotation. In a modification, the inner face of each piston is, instead of having the annular recess 131, is formed with a semi-cylindrical channel which when the faces are in contact, together form a diametrical passage. In a further construction the lower cylinder is the same as that in Figs. 7, 8 but the upper cylinder contains a single piston which engages the upper end of the left-hand shoe, the upper end of the right-hand shoe bearing on the closed end of the cylinder. With this arrangement, only the left-hand shoe is self-energising with both directions of drum rotation. A modification of this construction is shown in which to compensate for the relative inefficiency of the right-hand shoe when the drum rotates reversely, the piston which acts on the lower end of the left-hand shoe is of greater diameter than that of the other two pistons so that the left-hand shoe is more effective with reverse than with forward rotation of the drum. The inner face of the closed end of the cylinder in these latter constructions may be provided with an annular recess so as to form with the correspondingly shaped inner face of the piston an annular channel such as 131, Fig. 8, or the cylinder end face may be formed with a part cylindrical channel extending diametrically across it, the channel being open along its length adjacent the inner end face of the piston. The flexible sealing boot which is attached to the cylinder may instead of being also attached to the shoe end as shown in Figs. 1, 8, be attached to the end of the piston 157 as shown in Fig. 14, grooves being provided in the hub parts to receive the edges of the boot 160.